A wireless communication system typically includes a base station in wireless communication with a plurality of user devices (which may also be referred to as mobile stations, subscriber units, access terminals, etc.). The base station transmits data to the user devices over a radio frequency (RF) communication channel. The term “downlink” refers to transmission from a base station to a user device, while the term “uplink” refers to transmission from a user device to a base station.
Orthogonal frequency division multiplexing (OFDM) is a modulation and multiple-access technique whereby the transmission band of a communication channel is divided into a number of equally spaced sub-bands. A sub-carrier carrying a portion of the user information is transmitted in each sub-band, and every sub-carrier is orthogonal with every other sub-carrier. Sub-carriers are sometimes referred to as “tones.” OFDM enables the creation of a very flexible system architecture that can be used efficiently for a wide range of services, including voice and data. OFDM is sometimes referred to as discrete multitone transmission (DMT).
The 3rd Generation Partnership Project (3GPP) is a collaboration of standards organizations throughout the world. The goal of 3GPP is to make a globally applicable third generation (3G) mobile phone system specification within the scope of the IMT-2000 (International Mobile Telecommunications-2000) standard as defined by the International Telecommunication Union. The 3GPP Long Term Evolution (“LTE”) Committee is considering OFDM as well as OFDM/OQAM (Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation), as a method for downlink transmission, as well as OFDM transmission on the uplink.
The proposed OFDM-based modulation schemes, both on the uplink and the downlink, would require a relatively high peak to average power ratio (PAPR). This is because the amplitude of an OFDM signal is the summation of the amplitudes of the respective sub-carriers. As a result, the amplitude of an OFDM signal may change quite significantly. When a modulated signal with a high PAPR passes through an RF processing unit, the signal may be distorted due to the non-linearity of a regular RF amplifier.
A number of techniques have been proposed for reducing the PAPR of OFDM signals. One example of such a technique is tone reservation. With tone reservation, both the transmitting device and the receiving device agree on reserving a subset of tones (sub-carriers) for generating PAPR reduction signals. In other words, a tone reservation scheme holds a subset of tones “in reserve” to be solely used for PAPR reduction. The present disclosure relates to the issue of determining which tones are reserved for PAPR reduction and which tones are used for payload transmission.